Misfire-detecting system for internal combustion engines

A misfire-detecting system for an internal combustion engine having at least one spark plug, each having opposite ends, and an ignition secondary circuit connected to each of said at least one spark plug, comprising:

• reverse current-checking means provided in said ignition secondary circuit, for checking reverse current flowing in said ignition secondary circuit in a direction reverse to a direction of flow of current occurring when spark ignition takes place at said each of said at least one spark plug;
• misfire-detecting means for detecting occurrence of a misfire in said engine, based on voltage between said opposite ends of said each of said at least one spark plug assumed when spark discharge takes place at said each of said at least one spark plug;
• reverse current-detecting means for detecting said reverse current in said ignition secondary circuit;
• and
• abnormality-detecting means for detecting an abnormality of said reverse current-checking means, based on said reverse current detected by said reverse current-detecting means.